Mark Matthews, the United States navy captain who oversees the use of the Bluefin-21, told Guardian Australia on Monday that if the vehicle exceeded its limits more than once it would no longer work.

“It could probably go down further than that once, but it wouldn’t be functional after that,” he said.

There are other similar vehicles – often used for scientific research – that are capable of continuing the search if the seabed of the Indian Ocean turns out to be deeper than anticipated.

At the current search depth, the force of water is equivalent to an elephant’s mass applied to the area of a postage stamp.

Professor Ian Wright, director of science and technology at the National Oceanography Centre, said: “You’re talking about a third more pressure to go from 4,500m to 6,000m, where other AUVs are engineered to operate. They have thicker titanium casing and more compensation for the instruments inside.”